Move from MVC FAB menu to Superset React menu (#8289)

* adds react based menu for welcome view

* bump fab

* better logic in common_bootstrap_payload

* split up files

* fix spacing and module scope styles

* lint

* render correct template for welcome

tests/core_tests.py

@@ -90,7 +90,7 @@ class CoreTests(SupersetTestCase):
 
         # Testing overrides
         resp = self.get_resp("/superset/slice/{}/?standalone=true".format(slc.id))
-        assert "List Roles" not in resp
+        assert '<div class="navbar' not in resp
 
         resp = self.client.get("/superset/slice/-1/")
         assert resp.status_code == 404